The conformation and the electronic structure of 3-methoxythiophene (THOME) and 3-methylthiothiophene (THSME) have been determined by means of a multidisciplinary approach based on ultraviolet photoelectron and electron transmission spectroscopies and fully optimized ab initio 6-31G** and MP2/6-31G** calculations. The plots of the relative energy as a function of the X-Me torsion angle of THXME show that i) for both compounds the s-cis rotamer is an energy minimum lower in energy than the s-trans conformer; ii) the s-trans rotamer is a local minimum for THOME but a maximum for THSME; iii) the gauche conformer is calculated to be the lowest minimum for THSME but close to a maximum for THOME. These findings are rationalized in terms of a delicate balance of several effects such as the steric hindrance between the methyl group and the faced C-H group of the ring, the π*ring ← Xlp charge transfer interaction, the repulsion between the charge in the C2=C3 double bond and the in-plane heteroatom lone pair, the πring - Xlp interaction and C2-CMe electrostatic interaction. The possibility that these compounds can give rise to highly conducting polymers is briefly discussed.

Conformation and electronic structure of 3-methylchalcogenothiophenes

DISTEFANO, Giuseppe;DE PALO, Marcello;DAL COLLE, Maurizio;
1997

Abstract

The conformation and the electronic structure of 3-methoxythiophene (THOME) and 3-methylthiothiophene (THSME) have been determined by means of a multidisciplinary approach based on ultraviolet photoelectron and electron transmission spectroscopies and fully optimized ab initio 6-31G** and MP2/6-31G** calculations. The plots of the relative energy as a function of the X-Me torsion angle of THXME show that i) for both compounds the s-cis rotamer is an energy minimum lower in energy than the s-trans conformer; ii) the s-trans rotamer is a local minimum for THOME but a maximum for THSME; iii) the gauche conformer is calculated to be the lowest minimum for THSME but close to a maximum for THOME. These findings are rationalized in terms of a delicate balance of several effects such as the steric hindrance between the methyl group and the faced C-H group of the ring, the π*ring ← Xlp charge transfer interaction, the repulsion between the charge in the C2=C3 double bond and the in-plane heteroatom lone pair, the πring - Xlp interaction and C2-CMe electrostatic interaction. The possibility that these compounds can give rise to highly conducting polymers is briefly discussed.
1997
Distefano, Giuseppe; DE PALO, Marcello; DAL COLLE, Maurizio; Modelli, A; Jones, D; Favaretto, L.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11392/1201078
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